Thermapen, the fastest and most accurate probe you can get. Once again it ain't cheap, but all the competition guys (and Alton Brown) use it.
http://www.thermoworks.com/products/thermapen/
I also use a DigiQ controller for overnight cooks, it has a fan unit that will blow air on the coals when the temp drops. It keeps the temp rock solid throughout the entire cook time. Don't know if they make adapters for your grille, but you can probably ask. The setup has a leave in probe and it will alarm when it is done.
http://store.thebbqguru.com/weborderentry/DigiQ%20DX2
Guru makes a fancier one called the CyberQ wich is to compete with thr Rock's Stoker. They are fancier units with Wi-Fi datalogging and the ability to check your cook from your cell phone.
http://store.thebbqguru.com/weborderentry/CyberQ%20WiFi
https://www.rocksbarbque.com/